Plants and vegetable matter contain a range of compounds which are biologically active in humans providing beneficial physiological effects, including a reduction in the risks of cancer, heart disease and arthritis.
A range of bioactive compounds can be found in a wide variety of plant and vegetable material. Citrus fruits for example, contain bioactive compounds that can be included in two major groups; the limonoids and the flavonoids.
The limonoids are triterpenoid compounds which usually occur in citrus fruits. The limonoids may exist as aglycones, or be linked to a glucose molecule (the glucoside). The limonoid glucosides have recently been shown to possess powerful anti-cancer properties in animals.
The flavonoids are a group of benzopyran derivatives which occur widely in plants. The flavonoids typically consist of a benzene ring fused with a heterocyclic six-membered ring containing an oxygen atom. Many flavonoids may also exist as glycosides. In citrus fruits, the most predominant flavonoids are the flavanones, narirutin and hesperidin (in orange) and naringin (in grapefruit). These compounds are capable of lowering blood cholesterol levels in hypercholesterolemic individuals.
The flavonoids in citrus also include the polymethoxylated flavones. This group of compounds is represented by flavones substituted by methoxy groups and is unique to citrus. The polymethoxylated flavones have a wide range of physiological effects, including a very high antioxidant capacity, which has prompted investigations into their potential use as a potent anti-cancer agent and as an anti-inflammatory agent.
Polyphenolic compounds such as the citrus limonoids and citrus flavonoids occur in significantly higher concentrations in peel tissue when compared to the concentration in endocarp from which juice is extracted. The high concentrations of these compounds in the peel tissue help form the basis of the plant's protective mechanisms against bacteria, moulds, yeasts and insects.
Citrus peel is bitter, most often because of the presence of limonoid compounds in their aglycone form, and peel discharged from juicing operations is usually limed, pressed, dehydrated, pelletised and used as stock feed.
Recently, a commercial practice has arisen in the citrus processing industry to extract water soluble compounds from the peel of citrus fruits using a range of devices. The resultant dilute water extract (“juice”) is bitter and after clarification (or partial clarification) this juice is de-bittered by passing it over a synthetic polymer adsorbent. In this way, the bitter principles which are adsorbed to the polymer can be separated from the natural sugars and acids and some flavour compounds, which are not adsorbed to the polymer. Most limonoids and flavonoids however may also be preferentially adsorbed by the polymer along with the bitter principles. Treatment of the polymer with a caustic soda solution desorbs these compounds to regenerate the polymer. The treatment however also destroys the bioactive compounds, which are discharged as waste with the spent caustic soda solution.
One process for extracting bioactive components from citrus fruits has been described in PCT/AU01/01113 (WO 02/20112). In this process, a raw citrus extract is passed over a polystyrene-divinyl benzene polymer and bioactive compounds from the raw material are adsorbed onto the polymer. The bioactives are then sequentially eluted from the de-bittering polymer adsorbent by a constant gradient concentration of alcohol in an alcohol water mixture. Three separate alcoholic extracts containing limonoid glucosides, flavanone glycosides and polymethoxylated flavones are then able to be collected from the polymer adsorbent.
While this process enables the valuable bioactive compounds to be recovered from the adsorbent polymer, some mixing of the bioactive compounds in the eluent fractions can occur, leading to incomplete separation of the different bioactives from each other, in particular of the limonoid glucosides from the flavanone glycosides. This may result in a lower purity leading to formulation difficulties, for example.
It would be desirable to address some or all of these problems and to provide an improved process for obtaining bioactive compounds from vegetable material such as citrus fruits.